Actuator operated interlock switches require a tongue shaped actuator to be removed and inserted from a main switch housing. The switch is used to enable a power supply to machinery. The switch is generally mounted between a machine guard and a frame for the guard, with the tongue mounted to one of the guard and frame, and the main switch housing attached to the other of the guard and frame. The switch is designed such that the power supply cannot be enabled until the guard is closed and the tongue is thereby inserted in the main switch housing. In a switch with machine guard locking, the tongue cannot be removed from the switch housing and the guard opened until the machine has come to a stop or is in a safe condition for access thereto. In addition to the mechanical aspects of the switch, the switch additionally has several normally closed and normally opened safety contacts, the normally closed contacts enabling power when the guard is closed.
This type of switch has the disadvantage that personnel may override or bypass the safeguard provided by this switch by removing the tongue and inserting a foreign object into the switch to permanently bias it to its normal position where the contacts are closed and power is supplied. This is done to gain easier access to the machine, enabling the guard to be opened without the inconvenience of waiting for the machine to power down.